Ionization by energetic protons in Thermosphere-Ionosphere Electrodynamics General Circulation Model

Originating in the magnetosphere and precipitating into the high-latitude ionosphere, energetic protons in the keV energy range are a common auroral phenomenon and can represent an important energy source for the auroral atmosphere. In global models describing the ionosphere-thermosphere interaction, keV protons have always been neglected or treated as if they were electrons. Here we investigate the effect of keV protons on both the ionospheric and thermospheric composition in the E region on a planetary scale. We present a parameterization of electron and ion production rates induced by an incident proton beam as a fast computational scheme for use in global models. The incident proton beam is assumed to have a Maxwellian distribution with characteristic energies between 1 and 20 keV. The parameterization is validated against a full proton transport code. By including these parameterized electron and ion production rates in a one dimension-in-space (1D-in-space) Thermosphere-Ionosphere Global Mean Model, we show that proton precipitation can cause a significant enhancement of the electron density, the major ion (O-2(+) and NO+) densities, and the nitric oxide density. As a result, the conductivities in the E region are also greatly increased. Using the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM), we show that the proton precipitation, when added to the normal electron aurora, causes a large increase (up to 70%) in electron, O-2(+), and NO+ densities over much of the auroral oval. The NO density is affected in a larger area owing to the long lifetime of NO on the nightside. This first study of the influence of protons on a planetary scale clearly shows the significant impact that auroral keV protons can have on the ionospheric and thermospheric composition and the need to include proton precipitation in global models.